Thermal transfer printing is a type of non-impact printing in which controlled concentrations of heat are used to melt ink from a ribbon onto a print medium. The ribbon is a thin film or paper that readily transfers heat from its back face, which engages heating elements of a printing mechanism, to its front face, which is coated with a wax- or resin-bound ink. The print medium has a front face that is made to receive the melted ink.
One use of thermal transfer printing is for printing self-adhesive labels, which can be made with thermal transfer paper or film facestocks. The front face of the facestock must be absorptive to prevent the ink from smearing yet very smooth to prevent discontinuities in the printed image. Coating materials, such as calcium carbonate and calcinated clay pigments, are often used to increase absorptivity.
A back face of the facestock is coated with an adhesive for applying a length of the facestock to another article. A liner having a release coating protects the adhesive and allows the facestock to be wound into a roll of label stock prior to use. The liner also allows the facestock to be divided into individual labels that are carried by the liner.
The thermal transfer ribbon and the lined facestock are fed from different spools into a thermal transfer printer. The front face of the ribbon is registered in contact with the front face of the facestock between a thermal print head and a platen. Under light pressure, heat from the print head causes the ink to melt from the ribbon and be absorbed by the facestock. The ribbon is rewound onto a take-up spool for disposal. Individually printed labels can be dispensed either separately from or together with the liner. In the former case, the liner is rewound onto a take-up spool for disposal. In the latter case, sections of the liner must be discarded individually after the labels are removed.
However, the liners do not readily degrade, and disposal can be expensive. The liners are relatively costly to make and account for up to 60 percent of the size and weight of label stock rolls. The additional weight increases shipping costs, as well as the weight of portable thermal transfer printers. Also, many printer dispensing failures occur because of difficulties separating labels from the liners.